The invention relates to a process for the selective hydrogenation of hydrocarbons (HC) containing three or more carbon atoms and having conjugated and/or cumulative double bonds and/or acetylenic triple bonds in monoene-containing mixtures of hydrocarbons having at least three carbon atoms in the liquid phase on fixedly disposed catalysts. Such HC mixtures are produced, for example, when processing mineral oil.
Prior to the further processing of such hydrocarbon mixtures, it is frequently necessary to free the mixtures of polyunsaturated and acetylenic compounds. It is expedient to hydrogenate these compounds. The invention has the purpose of rendering hydrogenation selective to avoid to a maximum extend any losses of monoenes by the formation of saturated hydrocarbons and, in some cases, by rearrangement into undesired, unsaturated isomers. The term "monoenes" as used herein refers to mono-ethylenically unsaturated compounds; i.e., compounds having a single double bond.
Such hydrogenations can be conducted by means of conventional fixed catalysts. Especially suitable are metals of group VIII and the first subgroup of the Periodic Table applied, for example, to pumice, clays, or silicates as the support material. Several processes are known wherein the selectivity is raised by chosen reaction conditions or by modification of the catalyst.
Advantageous methods are the "cold hydrogenation" at a relatively low temperature (German Pat. No. 1,568,542); the hydrogenation in the liquid phase with dissolved hydrogen (British Pat. No. 1,122,018), and the hydrogenation of dienes to monoenes on palladium catalysts in the presence of ammonia (Belgian Pat. No. 802,721).
It has, furthermore, been suggested to modify the catalysts with sulfur compounds. Thus, it is possible to obtain catalysts by treatment with thioethers, for example, which act selectively on the hydrogenation of acetylene (French Pat. No. 1,240,175). Catalysts doped with hydrogen sulfide are suitable for the selective hydrogenation of butadiene; however, they catalyze simultaneously the isomerization of, for example, butene-1 to butene-2 (French Pat. No. 2,355,792).
Also, the addition of carbon monoxide in small amounts catalyzes the isomerization of butene-1 to butene-2 in the presence of hydrogen on palladium catalysts (French Pat. No. 2,438,084).
The conventional methods are unsatisfactory, since a certain proportion of the unsaturated hydrocarbons in the hydrocarbon mixture is entirely hydrogenated and, in many cases, isomerization cannot be prevented. In the hydrogenation of butadiene in mixtures made up of C.sub.4 -hydrocarbons, for example, butene-1 is isomerized to butene-2.
There is, thus, the objective to develop a simple process for the selective hydrogenation of hydrocarbons having conjugated and/or cumulative double bonds and/or acetylenic triple bonds in monoene-containing mixtures of hydrocarbons having at least three carbon atoms; i.e., from 3 to 5 carbon atomes in the liquid phase on fixedly arranged catalysts, wherein the hydrogenated compounds are converted into monounsaturated compounds and are retained as such and, furthermore, wherein no isomerization of the monoenes occurs.